The inspection of container interiors, particularly beverage cans and other opaque containers requires imaging of all areas of the container from the top flange, past the sidewalls, to the bottom areas. Automated systems typically are required to inspect for 1 mm defects from the top to the bottom of the can. Prior art systems involve multiple inspection stations and/or multiple cameras focussed onto different sections of the can. These prior art systems require a high level of mechanical and optical complexity due to their multiple optics and camera stations. Critical alignments are necessary to combine several images or sectors into one composite to detect any and all defects in the can.
Diffused lighting systems have been used to light containers such as glass bottles, but in the multiple camera and multiple pass inspection systems, it is not necessary to have uniform lighting over the entire area to be inspected, only the area being inspected during the particular inspection pass.